Apparatus and method for enhanced solvent recovery from solvent extracted material

ABSTRACT

Apparatus and method for desolventizing particulate material having a solvent carried thereby wherein an upper indirect heating zone and a lower direct heating zone is provided. Each of the zones has a plurality of spaced apart horizontal trays for receiving particulate material. The trays define a vertical series of compartments through which the particulate material passes. Steam is provided to the particulate material indirectly in said indirect heating zone and directly in said direct heating zone are also included. An integral air tight flash chamber below the compartments enhances solvent recovery via vaporization of residual solvent from the condensed steam adhered to the particulate material traveling through the direct heating zone prior to discharge of the particulate material. The recovered residual solvent is delivered under pressure to a predetermined compartment in the direct heating zone provide heat for desolventizing the solvent-laden particulate material.

This is a continuation of U.S. application Ser. No. 09/391,333 filed onSep. 7, 1999, now U.S. Pat. No. 6,279,250.

TECHNICAL FIELD

This invention relates to a material treating apparatus and method, andmore particularly to an apparatus and method for heat treating a solventextracted oleaginous material for enhanced recovery of solvent and steamused in the heat treating process. The apparatus and method are alsoapplicable to the thermal treatment of other materials and to materialscontaining liquids adhering thereon.

BACKGROUND OF INVENTION

In the processing of oleaginous seeds to extract oil by solventextraction, the seeds are crushed, milled or otherwise fragmented (i.e.,made into cakes, flakes etc.) and are treated with a solvent to extractthe oil, leaving a solvent extracted material (i.e., a particulatematerial, e.g., a meal) in which vaporizable solvent remains. By heatingthe meal using steam both indirectly as by a heated surface and/ordirectly by intimate steam contact with the meal, the solvent is removedtherefrom by vaporization while the “wet” meal is dried and otherwiseprocessed to deactivate certain types of enzymes and to denatureproteins to thereby produce an edible substance.

The prior art generally discloses processes and apparatus wherein thematerial from which the solvent is to be removed progresses downwardlyas a bed through a column which is provided with spaced horizontalplates therein dividing the interior of the column into a verticalseries of compartments. In these compartments, the material is heatedand agitated, with the finished material discharged from the bottom ofthe column and the solvent being removed as an overhead vapor from thecolumn for subsequent condensing, with or without pre-conditioning ortreatment.

Present desolventizing practice includes counter-current processingusing a direct contacting flow of steam. Steam is distributed within thecolumn such that it condenses on the particulate material whilevaporizing some quantity of solvent adhered thereupon, further providingsensible heat to raise the temperature of the particulate material.

Generally, the moisture content of the particulate material exiting thedesolventizer is from about 15 to 25 weight percent and is a function ofprior solvent content, other moisture content, the ratio of direct steamto indirect steam used in the process, and the exit temperature. Dryingis generally required to produce commercially saleable meal, withmoisture reduction on the order of 25 to 33 percent being necessary soas to produce a commercial product having a moisture content of about10-12 weight percent.

A shortcoming of known desolventizing practice is a small butsignificant quantity of the moisture content needing to be removed fromthe meal exiting the desolventizer is solvent. Customarily, a portion ofthe residual solvent remaining with the meal after desolventizing isdriven off (i.e., vaporized) in subsequent drying steps, along with thecondensed steam adhered or carried by the meal exiting thedesolventizer.

Heretofore, no known desolventizing process or single apparatus hassatisfactorily minimized atmospheric solvent vapor discharge, reducedthe quantities of make-up to the recycle solvent stream and reduced thecapital and operating costs of desolventizing operations as contemplatedby the apparatus and process of this invention.

SUMMARY OF THE INVENTION

It is a first objective of the invention to provide an improvedapparatus and method for desolventizing a particulate material.

Another objective of the invention is to provide an improved apparatusand method for desolventizing a particulate material whereby solventsare substantially vaporized in an indirect heating zone and furthervaporized in a direct heating zone.

Another objective of the invention is to provide an improved apparatusand method for enhanced solvent vapor recovery from a particulatematerial having a solvent carried thereby, whereby particulate materialin a direct heating zone enters an integral air tight flash chamberpositioned below a live steam sparge tray prior to discharge of the“wet” solvent extracted material from the desolventizer.

Another objective of the invention is to provide an improved apparatusand method for more efficiently heat treating a solvent extractedmaterial to remove the solvent adhered thereto whereby residual solventvapor obtained in a flash chamber integral to a desolventizer isthermocompressed for entry into a direct heating zone.

According to a preferred embodiment of the present invention and infurtherance of aforementioned objectives, apparatus and method isprovided having an upper indirect heating zone and a lower directheating zone. Each of the zones has a plurality of spaced aparthorizontal trays for receiving particulate material. The trays of theindirect heating zone permit flow of solvent vapor theraround while thetrays of the direct heating zone allow a counter-current flow of solventvapor and steam therethrough. The trays define a vertical series ofcompartments through which particulate material passes. Separate meansfor providing steam to the particulate material indirectly in saidindirect heating zone and directly in said direct heating zone areprovided. An integral air tight flash chamber below the means forproviding steam heat to the particulate material directly in said directheating zone enhances solvent recovery via vaporization of residualsolvent from the condensed steam adhered to the particulate materialtraveling through the direct heating zone prior to discharge of theparticulate material for subsequent processing. Means for delivering thevaporized residual solvent under pressure to a predetermined compartmentin the direct heating zone provide heat for desolventizing theparticulate material.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross section of a desolventizing apparatusconstructed in accordance with this invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIG. 1, there is shown a desolventizing apparatus 10having a hollow, generally cylindrically shaped housing 12 which forms avertical column 14 divided horizontally into a vertical series ofcompartments 16 by trays 18 for cascadingly carrying solvent ladenmaterial 20. Each of the trays 18 has an opening through which theparticulate material 20 is passed downwardly (i.e., cascaded) from onecompartment to the next compartment in a controlled manner. The column14 is further equipped with agitation means (not shown) to maintain theparticulate material occupying each tray in adequate mixing motion, keepthe particulate material in a loose (i.e., non-agglomerated andsubstantially homogenous) condition, and ultimately move the particulatematerial in a thin layer towards the tray outlets. Agitators or sweeparms which move over the bottoms of the compartments at a slightdistance from the surface of said bottoms are contemplated and may bepowered by known drives and drive assemblies to effect horizontal orother suitable movement for the agitation means.

The vertical column 14 generally includes an upper indirect heating zone30 and a lower direct heating zone 50. The upper indirect heating zone30 should include five or less trays 18; four are shown in the drawing.In the upper indirect heating zone 30 the trays 18 (i.e.,pre-desolventizing trays 18A) are steam heated basket type trays whichpermit solvent vapors to flow around the trays at a low velocity andthereby minimize fines carried out of the column 14 with the solventvapor. This provides a “clean” solvent vapor and thereby obviates theneed for pre-treatment prior to condensing of such solvent vapors.

The lower direct heating zone 50 should include at least two trays 18;five are shown in the drawing. In the lower direct heating zone 50 thetrays 18 (i.e., main trays 18B) are hollow staybolt type trays whichpermit countercurrent steam stripping wherein the solvent vapors fromone direct heating zone compartment are vented to the next highestadjacent tray in the column. The bottom most tray of the direct heatingzone 50 is a sparge (i.e., steam injection) tray 52 equipped with avariable speed rotary valve 54 to maintain the particulate material 20at a predetermined level thereupon.

The upper indirect heating zone 30 of the desolventizing apparatus 10,above the upper most compartment, is provided with a dome like cap ortop portion 32 having a particulate material inlet 34 and a solventvapor outlet 36. In this zone 30 of the column 14, the indirect heatingis accomplished using steam as by heat exchange through a steam-jacketedwall or via hollow plate style equipment. Preferably the bottoms betweenthe various compartments of this zone 30 consist of two plates enclosinga steam space which is connected to a supply for steam (not shown) sothat the interior volume of the double-bottoms can be adjusted to thetemperature required in the desolventizing process. It should beunderstood that each individual bottom may have steam admitted theretoseparately or may be connected to a common steam source.

The indirectly heated zone 30 can have one or several trays 18A, but notmore than five, and is designed to heat the particulate material 20 tothe solvent boiling point and initiate the drying process. All solventvapors from the indirect heating zone are condensible.“Pre-desolventizing” in the steam heated basket trays 18A reduces theamount of sparge steam required in the direct heating zone 50 so as toreduce the moisture in the particulate material 20 proportionately,thereby reducing the steam duty for the dryer subsequently used to drythe particulate material 20.

In the lower direct heating zone 50 of the desolventizing apparatus 10,live steam, in condensing, gives off its latent heat of vaporizationwhich is imparted to the downwardly cascading solvent containing meal20. With this approach, almost all remaining solvent is vaporizedquickly and exits the column 14 at the solvent vapor outlet 36 to acondenser (not shown) where the substantially dust free solvent isthereafter condensed.

Below the lowermost compartment containing sparge tray 52, column 14 isequipped with an integral air tight flash chamber 56 for enhancing therecovery of solvent vapor within the apparatus to thereby minimizesolvent vaporization from the particulate material 20 during dryingoperations. While a single flash chamber 56 is illustrated, it will beunderstood that two or more trays are also contemplated. The flashchamber 56 includes a discharge device 58, preferably a rotary pressurelock discharge gate, which may alternately be a screw conveyor or otherfeed device regulated to discharge the same quantity of meal as is beingfed into the top compartment of the column. As a result, a relativelyconstant volume of meal can be maintained in the desolventizer.

The flash chamber 56 is evacuated using a vapor compressor, preferably asteam ejector or thermocompressor assembly 60. The steam ejectorassembly 60 ideally comprises an end suction ejector 62, wherein theflashed solvent enters axially, not perpendicularly, and has only amotive steam nozzle (not shown) impeding the flow of the furtherrecovered solvent through the venturi-shaped diffuser 62A, whichconverts the velocity energy of the steam into pressure energy forcompression of the solvent vapor. The assembly 60 is further providedwith clean-outs 64 positioned both up and down stream of the suction endejector 62.

The thermocompressor effectively pressurizes the solvent vapor withdrawnfrom the flash chamber 56 to the pressure level required forintroduction into the desolventizing apparatus 10, specifically at alocation near the top of the direct heating zone 50. As the solventvapors become superheated upon compression, they thereby possess excessheat energy which is used to heat the partly desolventized particulatematerial in the upper portions of the desolventizing apparatus.

Preferably, the hot solvent vapors coming from the thermocompressor areintroduced into a compartment within the desolventizer upwardly disposedtherein but below the uppermost compartment thereof, and preferably ator about the interface of the indirect 30 and direct 50 heating zones ofthe column 14. The floors (i.e., trays 18) of the compartments 16 abovethe one into which hot solvent vapors are introduced are preferablyporous so that the vapors will pass therethrough and into contact withthe meal in the compartment or compartments above the one into which thevapors are introduced. Vaporization of solvent adhering to theparticulate material during its passage through the desolventizer will,thereby, be effected by the hot solvent vapors passing therethrough.

In operation, solvent laden meal 20, preferably in flake form, isconveyed by known means and is introduced into the indirect heating zone30 of the desolventizing apparatus 10 at the meal inlet 34. The meal 20is received in the steam heated tray 18A of the first (i.e., top)compartment where it is heated and agitated so as to vaporize solventfrom the meal 20. The meal 20 progresses downward through thecompartments 16 of the indirect heating zone 30, giving up solvent vaporat each stage of the progression. The solvent vapor generally travelsaround, as opposed to through, the pre-desolventizing trays 18A, in anupward direction, and exits the column 14 at the solvent vapor outlet 36for subsequent condensing.

The meal 20 next proceeds to the direct heating zone 50 where it isreceived in spaced apart porous trays 18B. Steam for directly contactingthe meal 20 via the trays 18B is introduced into the lower portion ofthe direct heating zone 50 via a sparge tray 52. As the meal travelsdownwardly through this zone 50 in a cascading fashion, the sparge steamis condensed upon the meal 20, thereby further liberating solvent fromthe meal while generally increasing the moisture content of theparticulate material. A rotary pressure lock discharge gate 54 transfersthe “wet” meal into the underlying integral flash chamber 56 which ismaintained at a relatively low pressure compared to the compartmentthereabove such that the meal is unable to contain all the heat itoriginally possessed as heat of fluid, with the residual solvent andsteam being spontaneously evaporated. A thermocompressor 60 effectivelyevacuates the residual solvent vapor from the flash chamber 56 so as toprovide superheated solvent vapor for reintroduction into the upperportion of the direct heating zone 30 to reduce total steam consumptionand thereby aid in solvent recovery in the desolventizing apparatus.

It will be understood that the material to be processed as hereinabovespecified can include all oil bearing materials such as vegetable seeds,gains, nuts and like materials, cotton seed, soya beans, tung nuts,linseed, castor beans, copra, bone meal, meat scraps and the like. Theliquid adhering on the liquid extracted material to be treated includesbut is not limited to inorganic and organic solvents such as water,aqueous solutions, gasoline, hexane, mixed paraffins, aromatic solvents,alcohols, ketones, aldehydes and other polar and non-polar solvents.

While this invention has been described with reference to anillustrative embodiment, this description is not intended to beconstrued in a limiting sense. Various modifications of the illustrativeembodiment, as well as other embodiments of the invention, will beapparent to persons skilled in the art upon reference to thisdescription. It is therefore contemplated that the appended claims willcover any such modifications or embodiments as followed in the truescope of the invention.

What is claimed is:
 1. Apparatus for desolventizing particulate materialhaving a solvent carried thereby, comprising: (a) a particulate materialinlet and a particulate material outlet positioned at opposite ends ofan apparatus housing; (b) an upper indirect heating zone below saidparticulate material inlet and a lower direct heating zone above saidparticulate material outlet, each of said zones having a plurality ofspaced apart horizontal trays for receiving particulate material, saidtrays defining a vertical series of compartments through whichparticulate material passes; (c) means for transferring said particulatematerial from one of said trays to a vertically downwardly-spaced tray;(d) means for providing steam to said particulate material indirectly insaid indirect heating zone; (e) means for providing steam to saidparticulate material directly in said direct heating zone; (f) means foragitating said particulate material in each of said trays; (g) anintegral air-tight flash chamber below said means for providing steam toparticulate material directly in said direct heating zone so as toenhance solvent recovery via vaporization of residual solvent from steamwhich condensed and adheres to the particulate material as theparticulate material travels through said direct heating zone prior todischarge of said particulate material from said apparatus; (h) meansfor delivering, under pressure, the vaporized residual solvent to apredetermined compartment in said direct heating zone of said apparatusto provide heat for desolventizing the particulate material; and (i) asolvent vapor outlet having means for enabling flow capacity adequate tovent said vapor.
 2. Apparatus in accordance with claim 1 wherein thetrays of said indirect heating zone permit flow of solvent vaportherearound.
 3. Apparatus in accordance with claim 2 wherein the traysof said direct heating zone permit a counter-current flow of solventvapor and steam therethrough.
 4. Apparatus in accordance with claim 3wherein said means for agitating solvent extracted material in each ofsaid trays includes sweep arms driven by a centrally inserted rotaryshaft serving to impart horizontal movement to said sweep arms. 5.Apparatus in accordance with claim 4 wherein said sweep arms arepositioned about said shaft to move over the bottoms of saidcompartments of said apparatus.
 6. Apparatus in accordance with claim 5wherein said means for delivering the vaporized residual solvent underpressure to a predetermined compartment in said direct heating zone is athermocompressor.
 7. Apparatus in accordance with claim 6 wherein saidthermocompressor comprises an ejector.